1. Field of the Invention
The invention relates to a steering wheel to be rotationally operated when changing the advancing direction or retreating direction of a conveyance such as a vehicle.
2. Description of the Related Art
An example of steering wheels includes an air bag device which, when an impact is applied to a vehicle from ahead, protects a driver against such impact (see, for example, JP-A-2014-111426). As shown in FIG. 16, this steering wheel 50 includes a support member 51, a slider 52, a damper holder 53 and an elastic member 54. The support member 51, while being inserted in a bag holder 56 of the air bag device 55, is supported by a core metal 57 of the steering wheel 50. The slider 52 has a cylindrical shape and is placed on the support member 51 to be slidable longitudinally along the axis thereof. The damper holder 53 has an annular shape and covers part of the axial-direction area of the slider 52. The elastic member 54 includes an annular elastic main body 54a interposed between the slider 52 and damper holder 53. The elastic member 54 includes, in such portion thereof as adjoins the front side of the elastic main body 54a, an annular gap G extending in the peripheral direction of the elastic member 54. The gap G is constituted of an annular groove opened in the front end face of the elastic member 54.
In the above structured steering wheel 50, the air bag device 55 functions as a damper mass of a dynamic damper and the elastic main body 54a functions as a spring of the dynamic damper. Thus, when the steering wheel 50 vibrates in the vertical direction or in the right-and-left direction, the elastic main body 54a, while elastically deforming at the same or near to the frequency of such vibration, vibrates with the air bag device 55, thereby absorbing the vibration energy of the steering wheel 50. Such absorption suppresses (restricts) the vibration of the steering wheel 50.
However, as disclosed in JP-A-2014-111426, in the structure that the annular gap G is formed in the elastic member 54, when the steering wheel 50 vibrates, besides the elastic deformation of the elastic main body 54a, such portion of the elastic member 54 as faces the gap G deforms elastically in the gap G. After the vibration is suppressed by the elastic deformation of the elastic member 54, the steering wheel 50 vibrates in the vertical direction and in the right-and-left direction and also, as shown by the arrow in FIG. 16, oscillates with the elastic member 54 as the fulcrum thereof. This influences the frequency characteristics of the vibration suppressed by the elastic main body 54a, thereby making them unstable.
Here, the above phenomenon may also be suppressed by filling the whole periphery of the above gap. However, in this case, to a reacting force caused by the elastic deformation of the elastic main body 54a, there is added a reacting force caused by filling the gap G, thereby making the elastic member 54 hard to deform elastically. Thus, similarly to the above case, the frequency characteristics of the vibration are unstable.